1. Field of the Invention
This invention pertains to fluid pumps, and more particularly to apparatus for circulating water.
2. Description of the Prior Art
Water aeration is a common practice. For example, it is known to pump water from a pond or lagoon generally vertically into the air. As the water falls back to the pond, it forms a spray of droplets that absorb oxygen. This practice helps keep the pond high in dissolved oxygen, which is especially beneficial to industry and municipalities for aerobic water and sewage treatment processes. In addition to performing a biological function, a column or fountain of water also has high aesthetic appeal. For those reasons, many parks and commercial buildings are landscaped with ponds having water fountains.
Some prior water aerators employ centrifugal pumps to pump the water into the air above the pond. The centrifugal pump is usually mounted to a block of low density material, such that the block floats at or near the water surface with the pump extending below the block. An electric motor is mounted to the pump. The pump outlet is substantially vertical to force the water into the air. Although centrifugal pumps can produce relatively high pressures, their output volumes are relatively low. When used as aerators, centrifugal pumps can produce decorative patterns, but only at low volumes. Low volume is a major disadvantage of centrifugal pumps. In addition, centrifugal pump aerators are undesirably expensive and heavy.
Another serious problem with centrifugal aerators is that they are very susceptible to failed operation due to cavitation. Once the pump impeller cavitates, the output flow reduces to a negligible amount. It is a characteristic of the pump that it cannot recover to properly discharge water again after the cause of cavitation is eliminated unless the motor is stopped and restarted.
Another common design of water aerator utilizes a propeller mounted to an electric motor shaft. The electric motor and propeller are usually mounted to a float device that suspends the propeller a few inches below the water surface. Prior propeller type aerators are relatively inexpensive and compact, and they are capable of pumping greater quantities of water than centrifugal pumps. However, propeller type aerators suffer the major handicap of being unable to impart a high velocity to the pumped water. Any attempt to increase the velocity of the water leaving the propeller by means of a nozzle or similar restrictor causes a back pressure on the propeller and a drastic decrease in flow, so the water output stream collapses to a dribble. Consequently, prior propeller type aerators cannot produce the decorative patterns of centrifugal pump aerators. For instance, because the propeller aerator cannot produce a high vertical column of water, a cone-shaped deflector is often located in the water output stream. Water striking the deflector is diverted into a high volume umbrella-shaped pattern but having only a low height. Also, like centrifugal pump aerators, propeller type aerators are very susceptible to failure due to cavitation. Should cavitation occur, the aerator must be stopped and then restarted.
Some prior water aerators suffer a further handicap, which concerns fouling due to weeds and other waterborne debris entering the equipment. Screens and strainers are commonly used to filter most of the contaminants from the incoming water. However, the screens must be cleaned periodically, which results in undesirable maintenance costs. Some aerators are designed with screens protecting only the impeller or propeller, with the motor shaft remaining exposed. As a result, even if the impeller or propeller is protected, weeds and the like can wrap around the motor shaft, thereby adversely affecting performance. Ultimately, the aerator must be shut down for cleaning. It is also known to provide aerators with knives for cutting the weeds, but knives present potentially serious safety problems. The foregoing deficiencies of prior aerators have been overcome to a large extent by the aeration device described in co-pending U.S. patent application Ser. No. 333,267. However, the present invention represents further improvements in water aeration devices.